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Textbook
Introduction
1. ACT Math
2. ACT English
2.1 ACT English intro
2.2 Punctuation
2.3 Conventions of usage
2.3.1 Parts of speech
2.3.2 Commonly confused words
2.3.3 Subject-verb agreement
2.3.4 Verb tenses
2.3.5 A vs. an
2.3.6 Weight of adjectives
2.3.7 Pronoun-antecedent agreement
2.3.8 Misplaced modifiers
2.4 Sentence structure
2.5 Organization, unity, cohesion
2.6 Topic development
2.7 Knowledge of language
3. ACT Reading
4. ACT Science
5. ACT Writing
Wrapping up
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2.3.5 A vs. an
Achievable ACT
2. ACT English
2.3. Conventions of usage

A vs. an

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The a vs. an rule is one you’re probably already familiar with.

It still shows up on the ACT, often as a trap in answer choices. The goal is simple: make sure you don’t get tricked into changing a correct sentence.

Remember that the article adjectives a, an, and the identify nouns.

So here’s the rule. When deciding whether to use a or an:

  1. Look at the following word’s first sound
  2. If that word begins with a vowel sound, an should be used. Otherwise, use a

Example

Take a look at this example:

An exemption was made when an error was found in the test taken by a graduate student.

Exemption and error are both nouns that begin with a vowel sound, so an is used. Because graduate does not begin with a vowel sound, a is the right choice.

Below, blanks have been placed where an a or an an might go. Decide which article fits best.

__(1)__ very hungry sparrow picked desperately at __(2)__ obvious seed, frozen at __(3)__ angle that made it difficult to harvest.

Now, you try. Choose the correct article for each blank:

  1. a/an
  2. a/an
  3. a/an
(spoiler)

Answer:

  1. a
  2. an
  3. an

The word “very” begins with a consonant sound, so you use a. The other two words (“obvious” and “angle”) begin with vowel sounds, so you use an.

Exercise

Here’s how you’ll see this concept on the ACT.

A massive, angry rhino threatened the safari group.

A. NO CHANGE
B. A massive angry rhino
C. An massive, angry rhino
D. A massive and angry rhino

(spoiler)

Answer: A. NO CHANGE

The sentence is correct as written.

  • B and D test whether you know that two adjectives of equal weight should be separated by a comma. There’s nothing technically wrong with D, but it breaks the concision rule (don’t use more words than you need).
  • B is identical to A except it removes the comma, which is incorrect here.
  • C is the a vs. an trap. The next word, “massive,” starts with a consonant sound, so you need a, not an.

Remember, all you have to do is follow these two steps:

Key points

Know when to use “a” or “an” by doing the following:

  1. Look at the following word’s first sound
  2. If that word begins with a vowel sound, “an” should be used. Otherwise, use “a”

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